Typical cranes present the crane operator with a three degree-of-freedom manual control problem. That is, a crane operator manually controls the crane's boom angle (or luffing motion), the crane's hoist line which is connected to the crane's hook or load, and the crane's slew motion, i.e., the motion experienced by the load when the boom is swung right or left about its pivot point. However, some shipboard cranes present the operator with a five degree-of-freedom manual control problem. That is, in addition to controlling a crane's boom angle, hoist line and slew angle, the operator must also control (using foot pedals, for example) the vertical and horizontal position of a rider block. Cranes such as these are known in the art as being equipped with a rider block tagline system (RBTS).
The RBTS was originally installed on a crane to reduce the pendulation of the hoist line. Briefly, a rider block cooperates with (i.e., rides along) the crane's hoist line at a position above the crane's hook or load in order to control load pendulation. The rider block is positioned vertically by a rider block liftline passing over the boom's outboard tip and down to the rider block. The rider block is positioned horizontally by a pair of taglines that extend from the crane angularly back to the rider block. Currently, the operator must manually control the outhaul or inhaul of the liftline and taglines while simultaneously controlling the boom angle, hoist line and slew angle. The increased control complexity translates to increased training time/costs, increased chance of an error, and decreased number of capable operators as the average crane operator may never be able to master the five-degree-of freedom control problem.